A known suspension control apparatus is disclosed in JP2005-67549A. The suspension control apparatus disclosed includes air spring means provided at each of wheels on right and left sides and including a first air chamber and a second air chamber. The suspension control apparatus causes a total air volume of the air spring means to be constituted by only the first air chambers and by a sum of the first air chambers and the second air chambers. As a result, the suspension control apparatus disclosed achieves both the improvement of ride quality and ability to drive on a rough road, and securing of roll stiffness. According to the disclosed apparatus, even when one of the air spring means fails, the roll stiffness is still ensured since the total air volume can be constituted by only the first air chambers by means of the normal air spring means. That is, a communication passage is further provided for connecting the second air chambers to each other that are provided at the wheels on right and left sides, respectively.
A vehicle height adjusting apparatus of present days includes, as illustrated in FIG. 5, an air spring constituted by a main chamber (i.e., main air chamber) MC and a sub chamber (i.e., sub air chamber) SC, an adjusting valve MV allowing and prohibiting a communication of air between an air supply source PS and the main chamber MC, a switching valve CV allowing and prohibiting a communication of air between the main chamber MC and the sub chamber SC, and a height sensor HS all provided at each of the four wheels. The air supply source PS includes a drier to which dry air (air discharged from the air spring) is supplied or through which dry air passes at a predetermined flow speed or less as a condition required for the drier to recover, i.e., to be dried. Thus, a low-pressure tank LP and, when applicable, a high-pressure tank HP are applied for aiming to reduce a vehicle height adjustment time. Such tanks are disclosed in JP50-28589.
As illustrated in FIG. 5 and disclosed in JP50-28589, a conventional vehicle height adjusting apparatus includes a low-pressure tank and a high-pressure tank. In this case, however, a flow resistance of a piping connecting these tanks and the air spring is large and thus sufficient flow speed cannot be assured. Even if a sufficient tank volume is ensured, reduction of a vehicle height adjustment time is limited. For example, according to the vehicle height adjusting apparatus illustrated in FIG. 5, air discharged from the air spring is stored in the low-pressure tank LP for the purposes of reducing the vehicle height adjustment time. Then, while a condition required for recovery of the drier is being satisfied, the air stored in the low-pressure tank LP is continuously discharged to the atmosphere even after the completion of the vehicle height adjustment. However, a flow resistance of a piping connecting the low-pressure tank LP, and both the main chamber MC and the air supply source PS is large and thus a sufficient discharge amount per time unit cannot be ensured.
Thus, a need exists for a vehicle height adjusting apparatus which is not susceptible to the drawback mentioned above.